What was the biggest earthquake ever recorded?

The magnitude 9.5 Valdivia earthquake in Chile on 22 May 1960. It remains the largest measured since instrumental recording began and released roughly twice the energy of the next largest, the 1964 Alaska earthquake.

What was the deadliest earthquake in history?

The 1556 Shaanxi earthquake in China, with an estimated 830,000 deaths, far more than any instrumentally recorded event. Most of the population lived in dwellings carved into loess cliffs, which collapsed. In the instrumental era the deadliest is the 2004 Sumatra earthquake and tsunami, at around 227,900.

Could a magnitude 10 earthquake happen?

It is not considered possible on Earth. Magnitude scales with the area of fault that ruptures, and no continuous fault is long enough to produce a 10. Reaching it would require a rupture thousands of kilometres longer than any that exists.

The biggest earthquakes ever recorded

The largest earthquake ever recorded is the magnitude 9.5 Valdivia earthquake, which struck southern Chile on 22 May 1960. It ruptured roughly 1,000 kilometres of the boundary where the Nazca plate dives beneath South America and generated a tsunami that killed people in Hawaii, Japan and the Philippines. No earthquake since has come within half its energy release.

The ten largest since 1900

Instrumental records begin around 1900, so this is a list of the largest measured earthquakes, not the largest that have ever occurred. Magnitudes are moment magnitude as currently published by USGS; several have been revised as methods improved.

The ten largest earthquakes recorded since 1900
Magnitude	Location	Date	Deaths
9.5	Valdivia, Chile	22 May 1960	About 1,600
9.2	Prince William Sound, Alaska	28 March 1964	131
9.1	Sumatra, Indonesia	26 December 2004	About 227,900
9.1	Tohoku, Japan	11 March 2011	About 19,700
9.0	Kamchatka, Russia	4 November 1952	None recorded
8.8	Maule, Chile	27 February 2010	About 550
8.8	Off Ecuador	31 January 1906	About 1,000
8.7	Rat Islands, Alaska	4 February 1965	None recorded
8.6	Northern Sumatra, Indonesia	11 April 2012	10
8.6	Assam, Tibet	15 August 1950	About 1,500

Every one of these was a subduction-zone thrust event. That is not a coincidence: only a subduction interface offers a fault surface large enough to produce this much slip at once.

Magnitude and death toll are barely related. The 1960 Chile earthquake was the largest ever measured and killed around 1,600 people; the 2010 Haiti earthquake was magnitude 7.0, releasing under one thousandth of the energy, and killed well over a hundred thousand. What decides the toll is how many people live above the rupture, what their buildings are made of, and what time of day it happens.

What was the biggest earthquake ever recorded?: The magnitude 9.5 Valdivia earthquake in Chile on 22 May 1960. It remains the largest measured since instrumental recording began and released roughly twice the energy of the next largest, the 1964 Alaska earthquake.
What was the deadliest earthquake in history?: The 1556 Shaanxi earthquake in China, with an estimated 830,000 deaths, far more than any instrumentally recorded event. Most of the population lived in dwellings carved into loess cliffs, which collapsed. In the instrumental era the deadliest is the 2004 Sumatra earthquake and tsunami, at around 227,900.
Could a magnitude 10 earthquake happen?: It is not considered possible on Earth. Magnitude scales with the area of fault that ruptures, and no continuous fault is long enough to produce a 10. Reaching it would require a rupture thousands of kilometres longer than any that exists.

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